UIActivityIndicator。
UIActivityIndicatorView *activityIndicatior = [UIActivityIndicatorView alloc] initWithActivityIndicatorStyle: UIActivityIndicatorViewStyleWhiteLarge];
activityIndicator.center = CGPointMake(512, 384);
[self.view addSubview: activityIndicator];
[activityIndicator startAnimating];
[activityIndicator stopAnimating];
[activityIndicator removeFromSuperView];